9 research outputs found

    Substrate-dependent modulation of the enzymatic catalytic activity: Reduction of nitrate, chlorate and perchlorate by respiratory nitrate reductase from Marinobacter hydrocarbonoclasticus 617

    Get PDF
    The respiratory nitrate reductase complex (NarGHI) from Marinobacter hydrocarbonoclasticus 617 (Mh, formerly Pseudomonas nautica 617) catalyzes the reduction of nitrate to nitrite. This reaction is the first step of the denitrification pathway and is coupled to the quinone pool oxidation and proton translocation to the periplasm, which generates the proton motive force needed for ATP synthesis. The Mh NarGH water-soluble heterodimer has been purified and the kinetic and redox properties have been studied through in-solution enzyme kinetics, protein film voltammetry and spectropotentiometric redox titration. The kinetic parameters of Mh NarGH toward substrates and inhibitors are consistent with those reported for other respiratory nitrate reductases. Protein film voltammetry showed that at least two catalytically distinct forms of the enzyme, which depend on the applied potential, are responsible for substrate reduction. These two forms are affected differentially by the oxidizing substrate, as well as by pH and inhibitors. A new model for the potential dependence of the catalytic efficiency of Nars is proposed.Fil: Marangon, Jacopo. Universidade Nova de Lisboa; PortugalFil: Paes De Sousa, Patrícia M.. Universidade Nova de Lisboa; PortugalFil: Moura, Isabel. Universidade Nova de Lisboa; PortugalFil: Brondino, Carlos Dante. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Moura, José J. G.. Universidade Nova de Lisboa; PortugalFil: Gonzålez, Pablo J.. Universidade Nova de Lisboa; Portuga

    A new CuZ active form in the catalytic reduction of N2O by nitrous oxide reductase from Pseudomonas nautica

    Get PDF
    J Biol Inorg Chem (2010) 15:967–976 DOI 10.1007/s00775-010-0658-6The final step of bacterial denitrification, the two-electron reduction of N2O to N2, is catalyzed by a multi-copper enzyme named nitrous oxide reductase. The catalytic centre of this enzyme is a tetranuclear copper site called CuZ, unique in biological systems. The in vitro reconstruction of the activity requires a slow activation in the presence of the artificial electron donor, reduced methyl viologen, necessary to reduce CuZ from the resting non-active state (1CuII/3CuI) to the fully reduced state (4CuI), in contrast to the turnover cycle, which is very fast. In the present work, the direct reaction of the activated form of Pseudomonas nautica nitrous oxide reductase with stoichiometric amounts of N2O allowed the identification of a new reactive intermediate of the catalytic centre, CuZ°, in the turnover cycle, characterized by an intense absorption band at 680 nm. Moreover, the first mediated electrochemical study of Ps. nautica nitrous oxide reductase with its physiological electron donor, cytochrome c-552, was performed. The intermolecular electron transfer was analysed by cyclic voltammetry, under catalytic conditions, and a second-order rate constant of (5.5 ± 0.9) × 105 M−1 s−1 was determined. Both the reaction of stoichiometric amounts of substrate and the electrochemical studies show that the active CuZ° species, generated in the absence of reductants, can rearrange to the resting non-active CuZ state. In this light, new aspects of the catalytic and activation/inactivation mechanism of the enzyme are discussed

    Artefacts induced on c-type haem proteins by electrode surfaces

    Get PDF
    J Biol Inorg Chem (2011) 16:209–215 DOI 10.1007/s00775-010-0717-zIn this work it is demonstrated that the characterization of c-type haem containing proteins by electrochemical techniques needs to be cautiously performed when using pyrolytic graphite electrodes. An altered form of the cytochromes, which has a redox potential 300 mV lower than that of the native state and displays peroxidatic activity, can be induced by interaction with the pyrolytic graphite electrode. Proper control experiments need to be performed, as altered conformations of the enzymes containing c-type haems can show activity towards the enzyme substrate. The work was focused on the study of the activation mechanism and catalytic activity of cytochrome c peroxidase from Paracoccus pantotrophus. The results could only be interpreted with the assignment of the observed non-turnover and catalytic signals to a non-native conformation state of the electron-transferring haem. The same phenomenon was detected for Met–His monohaem cytochromes (mitochondrial cytochrome c and Desulfovibrio vulgaris cytochrome c-553), as well as for the bis-His multihaem cytochrome c 3 from Desulfovibrio gigas, showing that this effect is independent of the axial coordination of the c-type haem protein. Thus, the interpretation of electrochemical signals of c-type (multi)haem proteins at pyrolytic graphite electrodes must be carefully performed, to avoid misassignment of the signals and incorrect interpretation of catalytic intermediates

    Structural redox control in a 7Fe ferredoxin isolated from Desulfovibrio alaskensis

    No full text
    The redox behaviour of a ferredoxin (Fd) from Desulfovibrio alaskensis was characterized by electrochemistry. The protein was isolated and purified, and showed to be a tetramer containing one [3Fe–4S] and one [4Fe–4S] centre. This ferredoxin has high homology with FdI from Desulfovibrio vulgaris Miyazaki and Hildenborough and FdIII from Desulfovibrio africanus. From differential pulse voltammetry the following signals were identified: [3Fe-4S]+ 1/0 (E0â€Č = − 158 ± 5 mV); [4Fe–4S]+ 2/+1 (E0â€Č = − 474 ± 5 mV) and [3Fe–4S]0/− 2 (E0â€Č = − 660 ± 5 mV). The effect of pH on these signals showed that the reduced [3Fe–4S]0 cluster has a pKÊčredâ€Č = 5.1 ± 0.1, the [4Fe–4S]+ 2/+1 centre is pH independent, and the [3Fe–4S]0/−2 reduction is accompanied by the binding of two protons. The ability of the [3Fe–4S]0 cluster to be converted into a new [4Fe–4S] cluster was proven. The redox potential of the original [4Fe–4S] centre showed to be dependent on the formation of the new [4Fe-4S] centre, which results in a positive shift (ca. 70 mV) of the redox potential of the original centre. Being most [Fe–S] proteins involved in electron transport processes, the electrochemical characterization of their clusters is essential to understand their biological function. Complementary EPR studies were performed.Fil: Grazina, Raquel. Universidade Nova de Lisboa. Faculdade de CiĂȘncias e Tecnologia. Departamento de QuĂ­mica. REQUIMTE/CQFB; PortugalFil: Sousa, PatrĂ­cia M. Paes de. Universidade Nova de Lisboa. Faculdade de CiĂȘncias e Tecnologia. Departamento de QuĂ­mica. REQUIMTE/CQFB; PortugalFil: Brondino, Carlos Dante. Universidad Nacional del Litoral. Facultad de BioquĂ­mica y Ciencias BiolĂłgicas. Departamento de FĂ­sica; Argentina. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Centro CientĂ­fico TecnolĂłgico Santa Fe; ArgentinaFil: Carepo, Marta S. P.. Universidade Nova de Lisboa. Faculdade de CiĂȘncias e Tecnologia. Departamento de QuĂ­mica. REQUIMTE/CQFB; PortugalFil: Moura, Isabel. Universidade Nova de Lisboa. Faculdade de CiĂȘncias e Tecnologia. Departamento de QuĂ­mica. REQUIMTE/CQFB; PortugalFil: Moura, JosĂ© J. G.. Universidade Nova de Lisboa. Faculdade de CiĂȘncias e Tecnologia. Departamento de QuĂ­mica. REQUIMTE/CQFB; Portuga

    Hunter color dimensions, sugar content and volatile compounds in pasteurized yellow passion fruit juice (Passiflora edulis var. flavicarpa) during storage

    No full text
    Changes in Hunter L, a and b values, glucose, fructose and sucrose contents, concentration of four volatile compounds (ethyl butirate, ethyl caproate, hexyl butirate and hexyl caproate) and furfural, were studied in yellow passion fruit juice (Passiflora edulis var. flavicarpa) pasteurized at 75ÂșC/60s, 80ÂșC/41s or 85ÂșC/27s, during storage at room temperature (25&plusmn;5ÂșC) and refrigeration (5&plusmn;1ÂșC) for 120 days. While the sucrose content decreased, the glucose and fructose contents increased significantly over storage time. The Hunter L and b values behaved similarly, with a tendency to decrease over time, inversely to Hunter a value. Volatile compound concentrations also decreased over time, inversely to the furfural content. Pasteurization at 85ÂșC/27s resulted minimum changes in the studied passion fruit characteristics, while that at 75ÂșC/60s was the most harmful. Storage under refrigeration tended to keep the best quality characteristics of the juice.<br>Foi estudada a variação dos valores "L", "a" e "b" do sistema de Hunter, dos teores de glucose, frutose e sacarose, e da concentração de quatro compostos volĂĄteis (butirato de etila, caproato de etila, butirato de hexila e caproato de hexila) e furfural, em suco de maracujĂĄ-amarelo (Passiflora edulis var. flavicarpa) submetido Ă  pasteurização (75ÂșC/60 s, 80ÂșC/41 s e 85ÂșC/27 s), durante o armazenamento a temperatura ambiente (25&plusmn;5ÂșC) e refrigerada (5&plusmn;1ÂșC) por 120 dias. Enquanto os teores de sacarose diminuĂ­ram, aqueles de glucose e frutose aumentaram significativamente. Os valores "L" e "b" apresentaram comportamento semelhante, com tendĂȘncia a diminuir ao longo do tempo, inversamente ao valor "a". As concentraçÔes dos compostos volĂĄteis tambĂ©m diminuĂ­ram, exceto para o furfural. A pasteurização a 85ÂșC/27 s proporcionou as menores alteraçÔes nas caracterĂ­sticas estudadas, enquanto aquela Ă  75ÂșC/60 s foi a mais prejudicial. O armazenamento sob refrigeração apresentou melhor tendĂȘncia na manutenção das caracterĂ­sticas
    corecore